A wide variety of methods and solvents have been disclosed for use in recovering higher yields of hydrogen for recycling in various hydroprocessing treatments. Obtaining a higher yield and purity of hydrogen for a recycled feedstream allows the plant to operate more efficiently and minimize the hydrogen production capacity and therefore the capital required to construct and operate the hydrogen production facility.
It is well known in the art to employ liquid solvents to strip methane, acid gases and other hydrocarbon gases from a mixed process stream containing hydrogen. While it is possible to strip methane and other undesired gases from the stream to leave a relatively high purity hydrogen stream of 98%, or better, there are a number of parameters that must be taken into account in designing and operating a practical system. For example, certain solvents that are highly efficient, e.g., have a high solubility for methane and other gases, would not be considered practical choices because of their cost.
It is also known in the chemical industry to analyze the quality of feedstock and process streams utilizing advanced analytical chemistry, alone or in combination with advanced mathematical models, chemometrics and correlations. These methods and systems permit efficient and rapid recovery of data for operating processes. Existing industrial analytical and control systems thus provide means for real-time changes of operating conditions to maintain product quality and process efficiency.
It is therefore an object of the present invention to provide a method and apparatus in which one or more readily available “refinery solvents” are utilized in a counter-current flow stripping column to achieve the maximum purity of hydrogen in the recycle gas stream leaving the top of the column by selective absorption of one or more non-hydrogen compounds mixed with the hydrogen passing through the column.
As used herein, the term “refinery solvents” means any one or more compounds that are generated as product or by-product streams in the same refinery facility or other chemical processing facility as the feedstream in which the percent hydrogen content is to be enhanced, and that are readily available for diversion in the required quantities for use as a solvent to absorb or strip one or more compounds from the hydrogen-containing feedstream in the practice of the invention. Relevant processes would include liquid/gas separation processes.
It is a further object of the invention to provide apparatus and a method of operation that selectively controls the type, volume and flow rate of one or more refinery solvents in response to the real time analytical results of the gases moving through the stripping column in order to obtain a hydrogen stream of maximum purity from a refinery process.
It is yet another object of the invention to employ analytical instruments and a computer-controlled flow regulation system with appropriate software to achieve the maximum purity of hydrogen by the selection from one or more readily available refinery solvents of a liquid absorbent composition that affords maximum solubility for the non-hydrogen gaseous components in the feedstream to the stripping column.
Another object of the invention is to provide an integrated real-time feedstream analytical system to monitor and control solvent selection and solvent flowrate based upon the solubility and selectivity of feedstream solutes in the refinery solvent or solvents available for use in the hydrogen purification process.